Pete Stark, who has served 20 terms in Congress, is facing his first serious challenge in years.

Photo: Russell Yip, The Chronicle

Pete Stark, who has served 20 terms in Congress, is facing his...

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Dublin City Councilman, Eric Swalwell is going door-to-door informing constituents of his campaign to run for Congress on Thursday, May 3, 2012 in Castro Valley, Calif. He carries a list of the specific homes with registered voters he will visit. He has done 15,000 of these visits so far. Today he will visit 35 houses in Castro Valley.

Photo: Dania Maxwell, Special To The Chronicle

Dublin City Councilman, Eric Swalwell is going door-to-door...

Image 3 of 4

Dublin City Councilman, Eric Swalwell stands on a doormat while going door-to-door informing constituents of his campaign to run for Congress on Thursday, May 3, 2012 in Castro Valley, Calif. He has done 15,000 of these visits so far. Today he will visit 35 houses in Castro Valley.

Photo: Dania Maxwell, Special To The Chronicle

Dublin City Councilman, Eric Swalwell stands on a doormat while...

Image 4 of 4

Dublin City Councilman, Eric Swalwell is going door-to-door informing constituents of his campaign to run for Congress on Thursday, May 3, 2012 in Castro Valley, Calif. He has done 15,000 of these visits so far. Today he will visit 35 houses in Castro Valley.

It was a revealing moment for California Rep. Pete Stark, the irascible East Bay liberal who has forged a reputation as a firebrand during four decades in Congress.

The 80-year-old Democrat, in a meeting with Chronicle editors and reporters this week, appeared to be confused about Solyndra, the Fremont solar power company whose collapse has fueled Republican criticism of the Obama administration's energy policies this election year.

"I wish I had enough expense allowance to get one of those new S's that Solyndra's going to make down there - the electric car," Stark said, after being asked about the company. "They run $60,000 to $90,000."

Solyndra doesn't make electric cars - or anything else. It declared bankruptcy and shut down last year after receiving $535 million in government loan guarantees. The electric car company in Fremont is Tesla Motors, which took over part of the abandoned Nummi plant and will release its next car, the model S, this summer.

Stark's gaffe may have been dismissed in the past as a simple mistake. But it was only the latest in a string of confounding statements and unsubstantiated charges he has made in recent weeks, raising questions about his effectiveness as he seeks his 20th term in the U.S. House of Representatives.

Last month, at a candidates debate in the East Bay, Stark accused Eric Swalwell, his Democratic opponent in the June 5 primary election, of taking "hundreds of thousands of dollars" in bribes. At Tuesday's meeting at The Chronicle, Stark wrongly accused the newspaper's conservative columnist, Debra J. Saunders, of donating to Swalwell's campaign. In both cases, Stark was forced to apologize.

"I don't think he's fit to be in office," Swalwell said this week. The Dublin city councilman said he has seen Stark coming undone "before my eyes," demonstrating that the incumbent "was willing to say anything" to keep his post.

"But there was also a sense of being embarrassed," Swalwell said. "Anyone who served 40 years in Congress, you don't want to see them unravel in an undignified way."

Suddenly vulnerable

California's perfect storm of political change - legislative districts were redrawn by a citizen's commission rather than political parties and a voter-approved new primary system sends the two candidates with the most votes to the November general election, regardless of political party - has made the seemingly invincible Stark appear to be a surprisingly vulnerable candidate.

"The last time Pete Stark ran for office in a competitive race, they phone-banked with rotary phones," said Paul Mitchell, president of Redistricting Partners, a Sacramento political consulting firm. "He hasn't run a campaign since before 'The Candidate' was a movie," in 1972.

Stark's old 13th Congressional District, which stretched down the East Bay shoreline from the city of Alameda to Fremont, was one of the state's most-liberal bastions. Now he's in the redrawn 15th District, which includes the more moderate cities of Pleasanton and Dublin, as well as parts of his old district.

In addition, the state's new primary system makes Stark one of "the most endangered incumbents" in California's congressional delegation, said Larry Gerston, professor of political science at San Jose State University.

Stark's territory, where Democrats outnumber Republicans by 2 to 1, has become the "classic case of what people wanted in the 'top-two' primary," said political analyst Tony Quinn, co-author of the California Target Book, which studies state congressional races. "You have a virtually assured general election race between two Democrats in November."

Time catches up

Gerston said another factor is sculpting the race for California's longest-serving congressman: the ravages of time.

"Age affects people so differently," said Gerston. The age difference between California U.S. Sen. Dianne Feinstein and Stark is 18 months, he said, "but they're worlds apart - from physical appearances to actions."

Stark's caustic demeanor hasn't helped, with his outbursts underscoring "his reputation for saying things on the edge and offending people and being brash," Gerston said. "When you're younger, you can get away with it. As you get older, all you carry away is the bitterness, and it's painful to watch."

Critics of Stark say he seems unaware of how YouTube and social media can turn his gaffes and jaw-dropping attacks into damaging viral hits.

As a 40-year-old banker in his first run for Congress in 1972, Stark pounded the issue of age in his race against George P. Miller, an entrenched, 81-year-old opponent. Stark dismissed the elder lawmaker's ideas as "petrified" and called Miller's 30-year reign in Congress a "monument to the man's mistakes and failures over the last half century."

Echoes of the past

Stark's young opponent this year mirrors that message.

"I bring new energy and ideas, which are very much needed," said Swalwell, 31, who knocks on constituents' doors nearly every night. "We have a lot of fast-changing issues, two national laboratories. ... You need someone in Congress who's going to be up to speed, roll up their sleeves and work hard, and also live in the community."

Stark's full-time residence is 3,000 miles away from the district - on a Maryland estate with his third wife and children, a 16-year-old son and 10-year-old twins.

Defending his record, Stark told The Chronicle this week that it is "exemplary" and includes delivering "billions to the Bay Area" in appropriations. "Every piece of health legislation that has come out has generally had my imprimatur on it," he said.

Yet Stark struggled to name any specific legislation that he has ushered through Congress in the last decade.

The incumbent has some notable supporters, including Democrat Ro Khanna of Fremont, a former Obama administration trade official who has amassed nearly $1.4 million for a possible future run in the district.

Stark is "as sharp as ever," said Khanna. He held a fundraiser for Stark on April 30, which drew about 100 local activists and officeholders. "My sense of politics is that he's entitled to respect for his public service," Khanna said. "People should run on their vision and ideas, and he has substantive ideas."

Opponent's supporters

Newcomer Swalwell also has noteworthy supporters, including the entire City Council in Union City - a Republican, three Democrats and an independent.

Next week, Phil Wente of the Wente Vineyards winemaking family in Livermore is sponsoring a fundraiser for Swalwell. Wente's sister, Carolyn Wente Layton, is also supporting Swalwell. Her backing is significant: She was married to Stark until they divorced in 1991.

Swalwell said some Democratic Party stalwarts told him not to run in the district, that there was a "ladder" candidates needed to climb before they took on a formidable officeholder like Stark.

But the challenger, who has out-raised Stark in campaign contributions in three of the last four reporting periods, said the new rule is that, in California, "the House of Representatives does not take reservations. It's walk-in only."